ISSUE48: FEBRUARY-APRIL 2007
network of research and training centres/programmes
COMMENT
Climate change and the coming coastal catastrophe
By Peter F. Sale
In 2008, nearly half of all people live within 100km of a coast, 14 of our 17 largest cities are coastal, and migration into coastal communities is continuing. Over the next 50 years, the global population is expected to increase from 6.7 billion to about 9.2 billion people. Most of that growth will occur in poorer countries and in coastal communities.
Coastal marine ecosystems provide enormous value to these coastal communities, in the form of fisheries, other resources, and various environmental services. They provide the great majority of our fishery resources, such as cod, salmon, shrimp and lobster, but also algae, aquarium specimens, and novel pharmaceuticals. In some places they also provide building materials in the form of rock, sand, lime for cement making, and timber (from mangrove forests).
Environmental services include filtering of silt and pollutants flowing from the land, erosion protection for coastal settlements, provision of critical nursery habitats for many marine species, and a broad range of recreational opportunities. Tourism, a major economic engine that often depends on the environmental quality of coastlines, frequently generates most of a poorer country's GDP.
Coastal marine environments provide sites for ports, harbors and the trade they foster, sometimes provide new coastal land when they are dredged and filled, and usually serve as final repository for domestic, industrial, and agricultural wastes.
Worldwide, because of climate change and growing human use, most coastal marine ecosystems face catastrophic decline in their capacity to provide their goods and services. To avoid this cliff requires prompt implementation of far more effective management, and aggressive limitation of greenhouse gas emissions.
With every successive
report from the Intergovernmental Panel on Climate Change (IPCC 2007), the
trajectories of tracked changes in climate are seen to be as steep as, or
steeper than, the worst-case scenarios described in previous reports. Climate
is changing very rapidly, and greenhouse gases are largely responsible.
It is also clear that ecological and political inertias will combine to
ensure that substantial climate change will happen over the next 50 years,
even if the world acts promptly and aggressively to reduce emissions. Many
of these guaranteed changes directly affect the coastal ocean.
The facts of climate change are not fully known, but the case is now sufficiently clear that a manager who does not take climate considerations into account in planning management strategy is being irresponsible.
In many regions, ocean surface temperatures are warming and prevailing current patterns are changing.
Such changes have multiple impacts on coastal ecosystems. Geographic distributions of forage fish, plankton and the nutrients on which they depend are altered so that food webs are disrupted and food that larger fish depend on is no longer available to them. Direct physiological effects of warmer water mean that organisms' need for food may increase and their rates of growth may fall. Such multiple effects, acting differently on different species, provide for unexpected outcomes in the functioning of coastal ecosystems.
Fisheries scientists have documented recent declines in salmon yields in western Canada, and marked changes in distribution of species in the North Sea, that can be attributed to climate change. There is similar evidence from other regions, and UNEP now (Feb 08) predicts the worldwide collapse of fishery stocks due to the combined effects of climate change, over-fishing, and pollution.
In addition to warming of surface waters, climate change results in enhanced violence of tropical storms, in very slightly increased acidity of surface waters, and in rising sea levels. Each of these has major impacts on coastal marine environments. The increase in severity of storms will interact with the growing coastal population to produce increasing loss of lives and property. Hurricane Katrina's impact on New Orleans will unfortunately be repeated, and many coastal communities, lacking the resources of the USA, will be even more severely impacted than was the US Gulf Coast.
Ocean acidification, the "silent killer" of climate change impacts, is going to lead to a greatly reduced capacity, by a broad sweep of marine organisms including many phytoplankton, snails, clams, oysters, worms, sea urchins, starfishes and, most conspicuously, corals to build their calcium carbonate skeletons. And the calcium carbonate (limestone) structures that ultimately result from the building of these skeletons ? think white cliffs of Dover will be more prone to dissolve.
I recently joined 16 other marine scientists to publish (Science, 14 Dec 07) a detailed analysis of the likely fate for coral reefs. These economically and ecologically very important ecosystems are likely to disappear worldwide by 2050, being replaced by less productive rocky benches supporting far fewer species, unless we make major efforts to improve management, and aggressively cut back greenhouse gas emissions.
I'm not talking here
about the extinction of a species, but about the global loss of an entire
ecosystem.
Sea level rise acts to worsen impacts of high tides and storms on coasts,
but it also forces shallow coastline ecosystems to move upwards onto land
that will be largely occupied by us and unavailable to them. Valuable
mangrove forests and salt marshes, even if we begin to do a better job of
conserving them, are likely to be squeezed between deep water and
hardened, asphalt-covered shores.
And if sea level rise is not modest and gradual ?and there are plausible arguments that it may not be our coastal communities will be impacted so severely that disasters such as Katrina, or the Indonesian Tsunami of 2004 will appear to have been minor inconveniences.
Peter F. Sale is Assistant Director of UNU International Network for Water, Environment and Health (UNU-INWEH) and a tropical marine ecologist. This commentary was published in Le Scienze Web News. These are his personal views.
© 2008 United Nations University